Apparatus and System for an Active Star/Stub/Ring Controller Area Network Physical Layer Transceiver

1. A controller area network (CAN) node suitable for use in a ring redundant CAN network topology that includes a master CAN node N 0 and N ring CAN nodes Nn (n=1, 2, . . . N, where N is at least 3), interconnected in a ring topology by N+1 CAN bus segments, with bus segment CAN( 1 ) connecting master CAN node N 0 to ring CAN node N 1 , bus segment CAN(N) connecting ring CAN node N(n−1) to ring CAN node Nn, and bus segment CAN(N+1) connecting the last ring CAN node NN to master CAN node N 0 , each ring CAN node Nn comprising: redundant CAN PHY An and CAN PHY Bn physical layer circuits, (n=1, 2, . . . N, where N is at least 3), to respectively interface to CAN bus segments CAN(N) and CAN(N+1); the CAN PHY An and Bn circuits each including a TXD (transmitter dominant) circuit and a RXD (receiver dominant) circuit; the CAN PHY Bn TXD circuit to transmit over a respective CAN(N) bus segment a TXD data signal with differential CAN dominant/recessive states; the CAN PHY Bn RXD circuit to monitor the respective CAN(N) bus segment, and generate an internal RXD signal corresponding to dominant and recessive states of the monitored CAN(N) bus segment; and the CAN PHY An TXD circuit to transmit over a respective CAN(N+1) bus segment a TXD data signal with differential CAN dominant/recessive states; the CAN PHY An RXD circuit to monitor the respective CAN(N+1) bus segment, and generate an internal RXD signal corresponding to dominant and recessive states of the monitored CAN(N) bus segment; and each RXD circuit including an RXD DTO (dominant time out) circuit configured to monitor the internal RXD signal, and detect a DTO stuck-dominant condition if the internal RXD signal is in a dominant state for greater than a pre-defined DTO stuck-dominant time-out period, and operable if a DTO stuck-dominant condition is not detected, to generate an intermediate RXD signal corresponding to the internal RXD signal, including dominant and recessive states; if a DTO stuck-dominant condition is detected, to generate an intermediate RXD DTO signal in a recessive state; TXD An and Bn logic combiner circuits with respective TXD outputs connected respectively to the CAN PHY An and Bn circuits, to logically combine a common TXD data signal and the intermediate RXD signal cross-coupled from respectively the CAN PHY Bn and An RXD circuits, and generate a resulting TXD signal for input respectively to the CAN PHY An and Bn circuits; an RXD logic combiner circuit to logically combine respective intermediate RXD signals from respective CAN PHY A and CAN PHY B circuits, and generate a resulting RXD signal; a controller to provide the common TXD Data signal, and receive from the RXD logical combiner circuit, the logically combined RXD signal, such that, if a DTO stuck-dominant condition is detected by one of the RXD circuits, the controller receives the RXD signal corresponding to the intermediate RXD signal from the other RXD circuit.

2. The ring CAN node of claim 1 : wherein each TXD circuit comprises a transmit dominant (TXD) amplifier to drive CANH and CANL differential bus lines of the respective CAN(N) bus segment, and the TXD amplifier is driven by the resulting TXD signal.

3. The ring CAN node of claim 1 , each RXD circuit to generate, in response to detection of a DTO stuck-dominant condition, respective DTO stuck-dominant fault_A and DTO stuck-dominant fault_B signals; and the controller to receive from respective RXD circuits in respective CAN PHY An and Bn circuits, the respective DTO stuck-dominant fault_A and fault_B signals, enabling the controller to determine when a respective CAN(N) bus segment is in a DTO stuck-dominant condition.

4. The ring CAN node of claim 1 , wherein the RXD DTO circuit comprises: an RXD dominant transition detector coupled to an output of the RXD comparator; a timer that is triggered by the RXD dominant transition detector detecting a dominant RXD transition; an RXD dominant timer comparator, coupled to an output of the timer, that compares an output of the timer to a selected value, wherein an internal RXD dominant signal is changed to an RXD DTO recessive signal after a selected time interval has lapsed as measured by the RXD dominant timer comparator; and an RXD recessive transition detector, wherein the RXD recessive transition detector clears the timer when a recessive transition occurs on an RXD internal signal.

5. The ring CAN node of claim 1 , wherein the controller is selected from the group consisting of: a MCU with a MCU link layer function; a DSP with a DSP link layer function; a μP with link layer function; and a general processor with a link layer function, derived from the combined RXD signal.

6. The ring CAN node of claim 1 , wherein the RXD logical combiner circuit is an AND gate; and the TXD An and Bn logic combiner circuits are AND gates.

7. A system suitable for communication over a controller area network (CAN) with a ring topology between CAN nodes, comprising: a master CAN node N 0 ; and N ring CAN nodes Nn (n=1, 2, . . . N, where N is at least 3), the master CAN node N 0 and the ring CAN nodes Nn interconnected in a ring topology with N+1 CAN bus segments, with bus segment CAN( 1 ) connecting master CAN node N 0 to ring CAN node N 1 , bus segment CAN(N) connecting ring CAN node N(n−1) to ring CAN node Nn, and bus segment CAN(N+1) connecting the last ring CAN node NN to master CAN node N 0 , each ring CAN node Nn; each ring CAN node Nn including: redundant CAN PHY An and CAN PHY Bn physical layer circuits, (n=1, 2, . . . N, where N is at least 3), to respectively interface to CAN bus segments CAN(N) and CAN(N+1); the CAN PHY An and Bn circuits each including a TXD (transmitter dominant) circuit and a RXD (receiver dominant) circuit; the CAN PHY Bn TXD circuit to transmit over a respective CAN(N) bus segment a TXD data signal with differential CAN dominant/recessive states; the CAN PHY Bn RXD circuit to monitor the respective CAN(N) bus segment, and generate an internal RXD signal corresponding to dominant and recessive states of the monitored CAN(N) bus segment; and the CAN PHY An TXD circuit to transmit over a respective CAN(N+1) bus segment a TXD data signal with differential CAN dominant/recessive states; the CAN PHY An RXD circuit to monitor the respective CAN(N+1) bus segment, and generate an internal RXD signal corresponding to dominant and recessive states of the monitored CAN(N) bus segment; and each RXD circuit including an RXD DTO (dominant time out) circuit configured to monitor the internal RXD signal, and detect a DTO stuck-dominant condition if the internal RXD signal is in a dominant state for greater than a pre-defined DTO stuck-dominant time-out perioda, and operable if a DTO stuck-dominant condition is not detected, to generate an intermediate RXD signal corresponding to the internal RXD signal, including dominant and recessive states; if a DTO stuck-dominant condition is detected, to generate an intermediate RXD DTO signal in a recessive state; TXD An and Bn logic combiner circuits with respective TXD outputs connected respectively to the CAN PHY An and Bn circuits, to logically combine a common TXD data signal and the intermediate RXD signal cross-coupled from respectively the CAN PHY Bn and An RXD circuits, and generate a resulting TXD signal for input respectively to the CAN PHY An and Bn circuits; an RXD logic combiner circuit to logically combine respective intermediate RXD signals from respective CAN PHY A and CAN PHY B circuits, and generate a resulting RXD signal; a controller to provide, the common TXD Data signal, and receive from the RXD logical combiner circuit, the logically combined RXD signal, such that, if a DTO stuck-dominant condition is detected by one of the RXD circuits, the controller receives the RXD signal corresponding to the intermediate RXD signal from the other RXD circuit.

8. The system of claim 7 : wherein each TXD circuit comprises a transmit dominant (TXD) amplifier to drive CANH and CANL differential bus lines of the respective CAN(N) bus segment, and the TXD amplifier is driven by the resulting TXD signal.

9. The system of claim 7 , wherein each RXD circuit to generate, in response to detection of a DTO stuck-dominant condition, respective DTO stuck-dominant fault_A and DTO stuck-dominant fault_B signals; and the controller to receive from respective RXD circuits in respective CAN PHY An and Bn circuits, the respective DTO stuck-dominant fault_A and fault_B signals, enabling the controller to determine when a respective CAN(N) bus segment is in a DTO stuck-dominant condition.

10. The system of claim 7 , wherein the RXD DTO circuit comprises: an RXD dominant transition detector coupled to an output of the RXD comparator; a timer that is triggered by the RXD dominant transition detector detecting a dominant RXD transition; an RXD dominant timer comparator, coupled to an output of the timer, that compares an output of the timer to a selected value, wherein an internal RXD dominant signal is changed to an RXD DTO recessive signal after a selected time interval has lapsed as measured by the RXD dominant timer comparator; and an RXD recessive transition detector, wherein the RXD recessive transition detector clears the timer when a recessive transition occurs on an RXD internal signal.

11. The system of claim 7 , wherein the controller is selected from the group consisting of: a MCU with a MCU link layer function; a DSP with a DSP link layer function; a μP with link layer function; and a general processor with a link layer function, derived from the combined RXD signal.

12. The system of claim 7 , wherein the RXD logical combiner circuit is an AND gate; and the TXD An and Bn logic combiner circuits are AND gates.

13. The ring CAN node of claim 1 , the CAN PHY An and Bn circuits further including a silent signal inputs that determine that the movement of messages from the master CAN node N 0 back to the master CAN node N 0 is one of clockwise and counterclockwise.

14. The ring CAN node of claim 3 , wherein, in response to the fault_A and fault_B signals, the controller is operable to signal a fault condition through a selected one of the CAN PHY An and Bn TXD circuits for transmission back to the master CAN node N 0 ; and receive from the master CAN node N 0 commands to identify the ring CAN node Nn that is a source of the stuck-dominant fault.

15. The system of claim 7 , the CAN PHY An and Bn circuits further including a silent signal inputs that determine that the movement of messages from the master CAN node N 0 back to the master CAN node N 0 is one of clockwise and counterclockwise.

16. The system of claim 9 , wherein, in response to the fault_A and fault_B signals, the controller is operable to signal a fault condition through a selected one of the CAN PHY An and Bn TXD circuits for transmission back to the master CAN node N 0 ; and receive from the master CAN node N 0 commands to identify the ring CAN node Nn that is a source of the stuck-dominant fault.